bmxtranswrap: add options to overide properties
bmxtranswrap: add options to overide properties

User can override the image aspect ratio, audio locked flag,
audio reference level and audio dialnorm.

ebu/ebu-bmx,xunchangguo/BMX,kierank/bmxlib-bmx,stuarthicks/bmx,xunchangguo/BMX,Limecraft/ebu-bmx,Limecraft/ebu-bmx,xunchangguo/BMX,ebu/ebu-bmx,stuarthicks/bmx,kierank/bmxlib-bmx,stuarthicks/bmx,kierank/bmxlib-bmx,ebu/ebu-bmx,Limecraft/ebu-bmx